<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            width: 200px;
            height: 200px;
            background-color: blanchedalmond;
            margin: 200px auto;
            position: relative;
            padding-top: 20px;
        }
        .son1{
            width: 50px;
            height: 50px;
            background-color: blueviolet;
            position: absolute;
            top:0px;
            margin-top: 200px;
        }
    </style>
</head>
<body>
    <div class="box">
        <div class="son1"></div>
    </div>
</body>
</html>
<script></script>